Video conferencing involves the capture and transfer of an image from a source location to a destination location. In most instances, video conferencing equipment is provided at both locations to permit the conferencees to see and hear each other as they are conferring in real time. In such applications, capturing the video images typically involves using a motion camera having a high-bandwidth output port which is used to transmit signals representing the captured images.
In terms of external appearance, such motion cameras can be similar to the cameras widely sold to consumers in retail stores. Both types are sufficiently compact in design to be portable or hand-held. Moreover, both types have a lens, a view finder, zoom controls, manual control switches and a signal output port. The signal output port on such motion cameras connects to a cable for carrying the output video signal to a display or editing equipment. Internally, however, the circuits used inside a video conferencing motion camera can be significantly different depending on the implementation used. The reasons for these differences are addressed below.
When using a motion camera for video conferencing, permitting the conferencees to see and hear each other in real time typically requires a special mechanism for transferring high volumes of digital data over the communication link (e.g., telephone line). In many real-time applications, the video images are of sufficient detail and/or quantity that the data representing the video images cannot be accurately transmitted by such conventional transmission media.
In view of this data-transmission concern, there have been various implementations attempting to overcome this problem.
One approach uses a relatively inexpensive low-bandwidth cable link between a conventional motion camera and an external computer system. This implementation uses a conventional hand-held camera having an analog VHF (television-type) signal-output port which provides analog data representing the captured video images to a conventional television-type input port to a computer system. The computer system then displays the received video information on a display monitor and, using a conventional or proprietary data-compression computer program, compresses the video image data before it is transmitted over a more conventional (low-bandwidth) communication link, such as a standard or upgraded telephone line. The compressed data is then received at the remote location and decompressed by another computer system using a decompression algorithm which corresponds to the previously-executed compression algorithm.
Another approach employs a relatively expensive high-bandwidth, data-communication link between the motion camera and an external computer system. In this implementation, unlike the conventional hand-held camera which includes an analog VHF (television-type) signal-output port, the motion camera includes a special interface circuit and signal output port which provides data representing the captured video images in digital form. The high-bandwidth, data-communication link then carries the digital video data to a specially-designed interface port and circuit in the computer system without causing significant degradation of the transmitted data. The computer system decodes the information for display, and then compresses the received video information for transmission over a conventional (low-bandwidth) communication link, as described above.
Yet another approach, which is useful in limited applications, involves discarding significant amounts of the captured digital video data (e.g., using a decimation algorithm) so that the data can be transmitted from the camera without requiring the expensive high-bandwidth communication link and associated interface circuitry. The applications for this approach are limited because discarding some of the captured video data results in an inaccurate reproduction (or display) of the video image at both the transmitting and the receiving ends of the video conference.
Such known video compression and decompression systems have experienced problems. For example, those implementations having specially-designed motion cameras use specifically-tailored hardware integrated circuits which require a burdensome amount of the limited real-estate available in such a motion camera. Further, widespread sales of such implementations are problematic because they are capable of operating with only one of the many types of available compression/decompression algorithms or they require a high-cost modification involving the addition of different peripheral items to accommodate the various compression standards. These standards include MPEG, MPEG1, MPEG2, JPEG, H.263, H.261, and Fractal, and there also are a number of other proprietary standards being used.
Yet another problem experienced by known video conferencing implementations is their need of various types of peripheral equipment to implement different image-capturing functions. For example, a system capable of handling the typical variety of applications typically includes the following items: a digital video camera for capturing full motion video; a digital still camera for capturing still pictures; a photo scanner; a black and white scanner; a business card scanner; a color scanner; a hand scanner; and a video capture card. The cost of such a system is further increased because these separate peripheral items often require their own unique interfaces to the computer system which interfaces with the telephone link.
Accordingly, there is a need for a cost-effective video-conferencing implementation that overcomes the above-discussed deficiencies.